Method for the production of lignin-containing precursor fibres and also carbon fibres

ABSTRACT

The invention relates to a method for the production of a precursor for the production of carbon—and activated carbon fibers according to the wet—or air-gap spinning method, in which a solution of lignin and a fiber-forming polymer in a suitable solvent is extruded through the holes of a spinning nozzle into a coagulation bath, the formed thread is stretched and subsequently treated, dried at an elevated temperature and then wound up. The lignin-containing thread is an economical starting material for the production of carbon—and activated carbon fibers.

This application is a U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/EP2012/059112, filed May 16, 2012,which claims priority under 35 U.S.C. §§119 and 365 to EuropeanApplication No. 11004131.6, filed May 18, 2011.

The invention relates to a method for the production of a precursor forthe production of carbon- and activated carbon fibres according to thewet- or air-gap spinning method, in which a solution of lignin and afibre-forming polymer in a suitable solvent is extruded through theholes of a spinning nozzle into a coagulation bath, the formed thread isstretched and subsequently treated, dried at an elevated temperature andthen wound up. The lignin-containing thread is an economical startingmaterial for the production of carbon- and activated carbon fibres.

Carbon fibres are high-performance reinforcing fibres which are usedessentially for composite materials in aircraft construction,high-performance vehicle construction (Formula I, high-performancesailing ships etc.), for sports equipment and increasingly for windenergy plants. Currently, extensive efforts are being made worldwide tointroduce carbon fibres of average quality (at a reduced price level)into mass applications in automobile construction, the development ofweight-reduced electric vehicles which is sought publicly in themeantime representing an essential driving force.

Carbon fibres are produced by heat treatment above 1,000° C. of organicprecursor fibres. The first carbon fibres were developed on the basis ofcellulose precursors and used as filaments in lamps. Nowadays,polyacrylonitrile or copolymers of polyacrylonitrile are the dominatingpolymers for the production of precursors for carbon fibres. The paletteof carbon fibres based on PAN is supplemented by high-modulus carbonfibre made from pitch. For PAN-based carbon fibres, the estimated annualcapacity in 2010 was at approx. 77,000 t and, for pitch-based carbonfibres, at 1,830 t (technical textiles March 2010). An overview of theproduction, the structure, the mechanical properties and also theapplication of PAN- and pitch-based carbon fibres is provided in: J. P.Donnet et al., Carbon fibers, third edition, Marcel Dekker, Inc. NewYork, Basle, Hong Kong.

Polyacrylonitrile and pitch are products of the petrochemical industryand hence are subject to the typical cost increase for this branch ofindustry. In the last few years, a development trend for developingprecursors which are not linked to the oil price with respect to the rawmaterials resulted therefrom. This trend was forced by the demand forcarbon fibres in the average quality segment and hence also in theaverage price segment for mass applications, as are seen in automobileconstruction.

Also biopolymers thereby came into focus. Reference was made already tocellulose (rayon) as raw material for the first carbon fibre. AlsoLyocell fibres were examined as precursor (S. Peng et al., J. Appl.Polymer Sci. 90 (2003) 1941-1947). It was shown that the Lyocell-basedcarbon fibres have somewhat greater strength than the rayon-based fibresproduced under comparable conditions. 1 GPa for the strength and approx.100 GPa for the modulus of elasticity are however at a very low levelfor carbon fibres. In addition to the cellulose man-made fibre, alsocellulose natural fibres were tested as precursor for carbon fibre. M.Zhang et al. (Die Angewandte makromolekulare Chemie (Appliedmacromolecular chemistry) 222 (1994) 147-163) used sisal fibre asprecursor for carbon fibre production. With a strength of 0.82 GPa and amodulus of elastocity of 25 GPa, the carbon fibres produced therefromare at a very low level.

Another biopolymer which increasingly is gaining importance in precursordevelopment is lignin. Lignin is a polyaromatic polyol which is acomponent of wood and occurs in large quantities as a by-product ofcellulose production. The carbon proportion is at approx. 60-65%. Thechemical structure of lignin is determined by the type of wood used inthe cellulose process and also the method of cellulose digestion whichis applied. The main quantities of the resulting lignin are supplied forenergy use. With lignin, an extremely economical raw material isavailable in very large quantities and is in practice not fibre-formingin the unmodified form. One objective was the development of melt-spunlignin-containing precursors. J. F. Kadla et al. (Carbon 40 (2002)2913-2920) describe the production of lignin fibre by melt-spinning of acommercially available kraft lignin and also melt-spinning of a mixtureof lignin with low proportions up to 5% of polyethylene oxide (PEO).Processing of pure lignin requires a thermal pre-treatment whichincreases the raw material costs and, in mixtures, only smallproportions of PEO are possible since, with larger quantities of PEO,adhesion occurs in the stabilising process. The carbon fibres made fromthe melt-spun lignin-containing precursors had strengths of approx. 0.4GPa and moduli in the range 40-50 GPa and hence still do not fulfil themechanical characteristic values sought by automobile construction,strength approx. 1.7 GPa and modulus approx. 170 GPa.

Kubo et al. (Carbon 36 (1998) 1119-1124) describe a process for themelt-spinning of lignin, in which, in a pretreatment step, thenon-melting high-molecular components are removed from the lignin. In afurther publication, K. Sudo et al. (J. Appl. Polymer Sci., 44 (1992)127-134) describe the pretreatment of lignin with organic solvents withsubsequent melt-spinning of the chloroform-soluble fraction. The carbonfibres produced therefrom had merely a low strength level.

U.S. Pat. No. 7,678,358 claims acetylation of lignin as precursor oflignin melt-spinning without however giving any information relating tothe properties of the carbon fibres produced in this way. The state ofthe art shows that it is possible in principle to produce melt-spunlignin-containing precursors for carbon fibres. However it is also shownthat the property level of carbon fibre based on PAN or pitch is notachieved. The question remains open as to whether the ligninmodification required to make this suitable for melt-spinning does notagain offset the cost advantage of the economical raw material, lignin.

The object underlying the invention is to develop an economical methodfor the production of a lignin-containing precursor based on asolution-spinning method for the production of carbon- and activatedcarbon fibres.

Furthermore, it is the object of the present invention to indicate acorresponding lignin-containing precursor fibre. In addition, thepresent invention relates to further processing of the precursor fibresto form carbon fibres and also correspondingly produced activated carbonfibres.

This object is achieved with respect to the method for the production ofa lignin-containing precursor fibre by the features of patent claim 1.Patent claim 14 relates to a correspondingly produced precursor fibre.In addition, a method for the production of a carbon fibre is indicatedby patent claim 16, with patent claim 18 a correspondingly producedcarbon fibre is provided.

In the case of the method according to the invention for the productionof a lignin-containing precursor fibre for the production of carbonfibres and/or activated carbon fibres, a solution, comprising at leastone sort of lignin and also at least one fibre-forming polymer selectedform the group consisting of cellulose or cellulose derivates in atleast one solvent, selected from the group consisting of tertiary amineoxides, ionic Liquids, aprotic polar solvents, dimethyl formamide and/ordimethyl accetamide is introduced into a coagulation bath by extrusionof the solution through a spinning nozzle by the wet spinning or air-gapspinning method, the lignin-containing precursor fibre precipitating.

In the method according to the invention, the preferably low processingtemperature of the solution, once produced, during extrusion thereofinto the coagulation bath is particularly advantageous, the maximumupper limit of this temperature being prescribed by the nature of thecoagulation bath (boiling point). Generally, the temperature of thecoagulation bath is hence below 100° C. As a result, extremely gentleprocessing of the lignin fibres is provided, which surprisingly leads tothe carbon fibres produced from these precursor fibres havingsignificantly increased tensile strength.

There is understood, according to the invention, by the term “solution”that all the components of the solution, i.e. both the lignin and thefibre-forming polymer, are completely solvated by the solvent. However,this term likewise also includes the possibility that the lignin fibresand/or the fibre-forming polymer are present partly undissolved herein.

A preferred embodiment of the method provides that the solution used instep a) is produced by agitation or kneading of the at least one sort oflignin and also of the at least one fibre-forming polymer in the atleast one solvent, preferably at temperatures of 60° C. or more,particularly preferred of 80° C. or more.

Furthermore, it is advantageous if the solution is filtered beforeintroduction into the coagulation bath, any possibly contained insolublecomponents being able to be separated.

In a particularly preferred embodiment, the spinning hole diameter ofthe spinning nozzle is from 50 to 600 μm, preferably 100 to 500 μm.

The methods for shaping the solution and transferring it into theprecipitation bath or coagulation bath are thereby effected in thewet-spinning method or in the air-gap spinning method, the air gap inthe case of an air-gap spinning method being preferably at least 10 mm,further preferred at least 20 mm and at most 500 mm.

Further advantageous aspects of the method according to the inventionprovide that the lignin-containing fibre according to step b)

-   a) is stretched, preferably is stretched to at least 1.1 times,    further preferred to 1.1 to 12 times, particularly preferred to at    least 1.5 times, particularly preferred to at least 2 times its    length, in particular at a temperature of at least 60° C.,    preferably at least 80° C., further preferred at least 90° C.,    particularly preferred of at least 100° C., the stretching being    implemented preferably in the precipitation bath, in air or in water    vapour,-   b) is washed, preferably washed with demineralised water,-   c) is treated subsequently with textile aids for improving the    thread strength and for avoiding electrostatic charges,-   d) is dried, in particular by winding up or winding round of the    fibre onto or around heated rollers and/or by through-flow drying at    a temperature of at least 80° C., preferably at least 100° C. and/or-   e) is wound up.

Furthermore, it is advantageously possible that the fibre is treatedwith a spinning oil before drying, after drying or before and afterdrying.

Preferred concentrations of the at least one sort of lignin are therebyfrom 1 to 99% by weight, preferably from 2 to 30% by weight,particularly preferred from 3 to 20% by weight, relative to the entiresolution.

Advantageous concentrations of the at least fibre-forming polymer arethereby, relative to the entire solution, from 1 to 99% by weight,preferably from 5 to 40% by weight, particularly preferred from 7 to 30%by weight, likewise relative to the entire solution.

In a particularly preferred embodiment, the coagulation bath compriseswater or a mixture of water and an organic liquid, such as aprotic polarsolvents, in particular dimethylsulfoxid (DMSO), such as aliphaticamides which are liquid at room temperature, in particulardimethylformamide (DMF) or dimethylacetamide (DMAc); tertiary amineoxides, in particular N-methylmorpholine-N-oxide; ionic liquids,preferably ionic liquids selected from the group consisting ofimidazolium compounds, pyridinium compounds or tetraalkylammoniumcompounds, particularly preferred 1-butyl-3-methylimidazolium chloride,1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetateand/or mixtures hereof.

An advantageous pH value of the coagulation bath is thereby between 1and 7, preferably between 2 and 5.

The solvent for the spinning solution, i.e. the solution which comprisesthe lignin and also at least one fibre-forming polymer, is therebyselected preferably from the group consisting of aprotic polar solventsin particular dimethylsulfoxide (DMSO) dimethylformamide (DMF) ordimethylacetamide (DMAc); tertiary amine oxides, in particular aqueousN-methylmorpholine-N-oxide (NMMNO, in particular NMMNO monohydrate);ionic liquids, preferably ionic liquids selected from the groupconsisting of imidazolium compounds, pyridinium compounds ortetraalkylammonium compounds, particularly preferred1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium acetate; and/or mixtures hereof

The fibre-forming polymers are selected from the group consisting ofcellulose and/or cellulose derivatives, in particular cellulosecarbamate, cellulose allophanate and hemicellulose and/or mixtures orblends hereof

Furthermore, it is advantageous in the case of the method according tothe invention if the at least one sort of lignin results from wood andannual plant pulping methods and is selected in particular from thegroup consisting of alkali lignin, kraft lignin, lignosulphonate,thiolignin, organosolvlignin, ASAM lignin, lignins from digestionprocesses by means of ionic liquids or enzymes and/or combinations ormixtures hereof.

According to the invention, a precursor fibre for the production ofcarbon fibres is likewise indicated. The precursor fibre according tothe invention is distinguished by

-   a) a content of at least one sort of lignin of 1% to 99% by weight,    preferably 20 to 60% by weight,-   b) a content of at least one sort of fibre-forming polymer of 1% to    99% by weight, preferably 40 to 80% by weight, and-   c) possibly a strength of at least 10 cN/tex, preferably at least 20    cN/tex, and-   d) possibly a modulus of elasticity of at least 1,000 cN/tex,    preferably at least 1,300 cN/tex.

The precursor fibre according to the invention can be producedparticularly advantageously according to a previously described method.

Concerning the definitions of lignin and the fibre forming polymers werefer to the method claims 12 and 13 and the description.

Furthermore, a method is indicated according to the present inventionfor the production of a carbon fibre, in which a precursor fibreaccording to one of the two preceding claims is stabilised attemperatures between 100 and 600° C. and is carbonised above 800° C.under inert conditions.

In a preferred embodiment, the carbon fibre is subjected to watervapour, after the carbonisation, at temperatures >200° C.,preferably >300° C.

In addition, the present invention provides a carbon fibre which can beproduced according to the previously described method for the productionof the carbon fibre.

The present invention is explained in more detail with reference to thesubsequent embodiments and examples without restricting the invention tothe represented parameters.

The lignin is preferably mixed with the thread- or fibre-forming polymerand then dissolved in a suitable solvent by agitation or by a kneadingprocess at an elevated temperature. The resulting solution is possiblyfiltered and then advantageously shaped to form filaments by wet- orair-gap spinning, which can be stretched under different conditions,washed, treated, dried and then wound up as a filament.

The different lignins, such as alkali lignin, lignosulphonate,thiolignin, organosolvlignin or types of lignin from alternative wooddigestion processes, which are known to the person skilled in the art,as occur during cellulose production or also mixtures of these can beused. The lignins are washed intensively with water or possibly alsowith diluted acids up to an ash content of less than 1%.

As fibre-forming polymers, in particular cellulose or also cellulosederivatives, such as cellulose carbamate and cellulose allophanate, areused.

As solvent, for example aliphatic amides, such as DMF or DMAc, DMSO,tertiary amine oxides, preferably aqueous N-methylmorpholine-N-oxide,particular NMMO monohydrate or an ionic liquid, selected from the groupconsisting of imidazolium compounds, pyridinium compounds,tetraalkylammonium compounds and mixtures hereof, are used.

The spinning solution is preferably produced with agitation or bykneading at a temperature above 60° C., preferably above 80° C. Thepolymer concentration is adjusted for example to greater than 8%,preferably greater than 10%. The resulting viscous solution can befiltered using normal filtration devices and can be supplied as ahomogeneous particle-free solution for intermediate storage before thespinning process.

The shaping of the spinning solution to form fibres or filaments iseffected according to the wet-spinning or air-gap spinning method. Inthe case of the wet-spinning method, the spinning solution is pressedthrough the holes of a spinning nozzle, spinning nozzles with holediameters of 50 to 500 μm being used. The extruded thread is solidifiedin the coagulation bath which consists of water or of a mixture of thepolymer solvent and a nonsolvent. The nonsolvent can be preferably wateror an aliphatic alcohol with a chain length up to C 8. When applyingair-gap spinning, the viscous lignin-containing spinning solution ispressed through the holes of a spinning nozzle and the extruded threadsare stretched in the air gap. The preferred nozzle hole diameter ispreferably greater than 100 μm and should not exceed 600 μm. The air-gaplength is at least 10 mm. The air-stretched thread is then coagulatedcomparably to wet-spinning.

The thread is stretched in water and/or a mixture of water and thesolvent at a temperature greater than 80° C., preferably greater than90° C. and in hot air and/or water vapour greater than 90° C.,preferably greater than 100° C. up to a multiple of its length but by atleast 1.1 times. The stretching can be effected before or even after thewashing process.

The stretched and washed thread is treated, before the drying or afterthe drying or before and after the drying, with a spinning oil with anantistatic effect. Drying is effected on heated rollers or also bythrough-flow drying at temperatures greater than 80° C., preferablygreater than 100° C.

The thus produced fibre comprises at least 10% lignin, preferably >20%lignin and one or more fibre-forming polymers, such as cellulose and/orcellulose derivatives, such as cellulose carbamate and/or celluloseallophanate. The fibres produced according to the invention have atensile strength of at least 10 cN/tex and a modulus greater than 500cN/tex and can be converted, according to known methods for stabilisingand carbonisation, into carbon fibres and also, by a subsequent watervapour treatment, into activated carbon fibres with a high specificsurface.

EXAMPLE 1

60 g of a cellulose (DP_(Cuox)=490) which comprises up to 12%hemicellulose are mixed with 29 g air-dried organocell lignin in 500 g1-butyl-3-methylimidazolium chloride and dissolved in a horizontalkneader at a temperature of 90° C. within 3 h. The resulting black,homogeneous solution is free of fibre residues and has a zero shearviscosity, measured at 80° C., of 578 Pas.

The solution was pressed through a 40-hole spinning nozzle (holediameter 200 μm) with the help of an extruder stretched with a drawingratio of 14 in the air gap and the filaments were precipitated in theacetic acid coagulation bath (pH=2.5). Washing of the filaments waseffected with distilled water, drying was effected in air. The filamentshad a strength of 25 cN/tex, an elongation of 7.6% and also a modulus ofelasticity of 1,320 cN/tex. The lignin content was 20.3%.

EXAMPLE 2

75 g of an air-dried chemical cellulose (DP_(Cuox)=560) are mixed with48 g air-dried kraft lignin in 500 g 1-ethyl-3-methylimidazolium acetateand dissolved in a horizontal kneader at a temperature of 90° C. within3 h. The resulting black, homogeneous solution is free of fibre residuesand has a zero shear viscosity, measured at 100° C., of 374 Pas. Thesolution was pressed through a 40-hole spinning nozzle (hole diameter200 μm) with the help of an extruder, stretched with a drawing ratio of18 in the air-gap and the filaments were precipitated in the aqueouscoagulation bath. Washing of the filaments was effected with distilledwater, drying was effected in air. The filaments had a strength of 28cN/tex, an elongation of 9.6% and also a modulus of elasticity of 1,560cN/tex. The lignin content was 36.4%.

EXAMPLE 3

30 g cellulose carbamate (DP_(Cuox)=258, DS=0.4) are mixed with 10 gair-dried organosolvlignin and 70 g 1-butyl-3-methylimidazolium acetateand dissolved in a horizontal kneader at a temperature of 110° C. within2 h. The resulting black, homogeneous solution is free of fibre residuesand has a zero shear viscosity, measured at 100° C., of 1,215 Pas. Thesolution was pressed through a 12-hole spinning nozzle (hole diameter150 μm) with the help of an extruder, stretched with a drawing ratio of30 in the air gap and the lignin-containing cellulose carbamate fibrewas precipitated in the aqueous coagulation bath with 15%1-butyl-3-methylimidazolium acetate. Washing of the filaments waseffected with distilled water, drying was effected in air. The filamentshad a strength of 45 cN/tex, an elongation of 6.4% and also a modulus ofelasticity of 2,346 cN/tex. The lignin content was 18.3%.

EXAMPLE 4

447 g of an air-dried chemical cellulose (DP_(coux)=560) are mixed with276 g air-dried kraft lignin and also 2.1 g propylgallate in 5.2 kg 52%N-methylmorpholine-N-oxide hydrate and dissolved in a horizontal kneaderat a temperature of 90° C. with distillative water separation within 3h. The resulting black, homogeneous solution is free of fibre residuesand has a zero shear viscosity, measured at 90° C., of 642 Pas. Thesolution was pressed through a 40-hole spinning nozzle (hole diameter200 μm) with the help of an extruder, stretched with a drawing ratio of20 in the air gap and the filaments were precipitated in the aqueouscoagulation bath. Washing of the filaments was effected with distilledwater, drying was effected in air. The filaments had a strength of 42cN/tex, an elongation of 5.4% and also a modulus of elasticity of 2,164cN/tex. The lignin content was 52.4%.

The invention claimed is:
 1. A method for the production of alignin-containing precursor fibre for the production of carbon fibresand/or activated carbon fibres, comprising a) forming a solution,comprising at least one variety of lignin and also at least onefibre-forming polymer selected from the group consisting of cellulose orcellulose derivatives, in at least one solvent selected from the groupconsisting of tertiary amine oxides, and mixtures thereof, and b)transferring the solution into a coagulation bath by extruding thesolution through a spinning nozzle by a wet spinning or an air-gapspinning method to form the lignin-containing precursor fibre, whereinthe lignin-containing precursor fibre precipitates when the solution isextruded, and c) stretching the lignin-containing precursor fibre to atleast 1.1 times its length, at a temperature of at least 60° C. in thecoagulation bath, in air, or in water vapour.
 2. The method according toclaim 1, wherein the solution formed in step a) is produced by agitationor kneading of the at least one variety of lignin and also of the atleast one fibre-forming polymer in the at least one solvent, attemperatures of 60° C. or more.
 3. The method according to claim 2wherein the temperature is above 80° C.
 4. The method according claim 1,wherein the solution is filtered before transferred into the coagulationbath.
 5. The method according to claim 1 wherein the tertiary amineoxide is aqueous N-methylmorpholine-N-oxide.
 6. The method according toclaim 1 wherein the cellulose or cellulose derivatives are selected ofthe group consisting of cellulose carbamate, cellulose allophanate,hemicelluloses, and mixtures thereof.
 7. The method according to claim 1wherein the at least one variety of lignin results from wood and annualplant pulping methods and is selected from the group consisting ofalkali lignin, kraft lignin, lignosulphonate, thiolignin,organosolvlignin, ASAM lignin, lignins from digestion processes by meansof ionic liquids or enzymes and combinations thereof.
 8. The methodaccording to claim 1 wherein the spinning nozzle has a spinning holediameter from 50 to 600 μm.
 9. The method according to claim 8 whereinthe spinning hole diameter of the spinning nozzle is between 100 and 500μm.
 10. The method according to claim 8 wherein the transferring step isperformed by the air-gap spinning method, wherein there is an air gap ofat least 10 mm and at most 500 mm.
 11. The method according to claim 10wherein the air gap is at least 20 mm.
 12. The method according to claim1 wherein the solution comprises, a) 2 to 30%, by weight, of the atleast one variety of lignin, and b) 5 to 40%, by weight, of the at leastone fibre-forming polymer.
 13. The method according to claim 12, whereinthe solution comprises between 3 and 20%, by weight, of the at least onevariety of lignin.
 14. The method according to claim 12 wherein solutioncomprises between 7 and 30%, by weight, of the at least onefibre-forming polymer.
 15. The method according to claim 1 wherein thecoagulation bath comprises water or a mixture of water and an organicliquid selected from the group consisting of aprotic polar solvents,aliphatic amides which are liquid at room temperature, tertiary amineoxides, and ionic liquids.
 16. The method according to claim 15 whereinthe ionic liquids are selected from the group consisting of1-butyl-3-methylimidazolium chloride, 1 -butyl-3-methylimidazoliumacetate, and 1-ethyl-3- methylimidazolium acetate.
 17. The methodaccording to claim 15 wherein the pH value of the coagulation bath isbetween 1 and
 7. 18. The method according to claim 17, wherein the pHvalue of the coagulation bath is between 2 and
 5. 19. The methodaccording to claim 1 wherein the lignin-containing precursor fibre d) iswashed with demineralised water, e) is treated subsequently with one ormore textile aids for improving the thread strength and for avoidingelectrostatic charges, f) is dried by winding up or winding round of thefibre onto or around heated rollers or by through-flow drying at atemperature of at least 80° C., and g) is wound up.
 20. The methodaccording to claim 19 wherein the fibre is treated with a spinning oilbefore being dried according to step f), after being dried according tostep f) or before and after being dried according to step f).
 21. Themethod according to claim 19 wherein the lignin-containing fibre isstretched to at most 12 times.
 22. The method according to claim 19wherein the lignin-containing fibre is stretched to at least 1.5 times.23. The method according to claim 19 wherein the lignin-containing fibreis stretched at a temperature of at least 80° C.
 24. The methodaccording to claim 19 wherein the lignin-containing fibre is stretchedat a temperature of at least 100° C.
 25. The method according to claim19 wherein the lignin-containing fibre is dried at a temperature of atleast 100° C.
 26. A method for the production of a lignin-containingprecursor fibre for the production of carbon fibres and/or activatedcarbon fibres, comprising: a) forming a solution, comprising at leastone variety of lignin and also at least one fibre-forming polymerselected from the group consisting of cellulose or cellulosederivatives, in at least one solvent selected from the group consistingof tertiary amine oxides, ionic liquids, aprotic polar solvents,dimethylformamide and dimethylacetamide, and mixtures thereof, and b)transferring the solution into a coagulation bath by extruding thesolution through a spinning nozzle by a wet spinning or an air-gapspinning method, wherein the lignin-containing precursor fibreprecipitates when the solution is extruded, wherein the pH value of thecoagulation bath is between 2 and
 5. 27. The method of claim 26 furthercomprising: c) carbonizing the lignin-containing precursor fibre atinert conditions and at a temperature above approximately 800° C. toform carbon fibers.
 28. A method for the production of carbon fibresfrom a lignin-containing precursor fibres comprising: forming asolution, comprising at least one variety of lignin and also at leastone fibre-forming polymer selected from the group consisting ofcellulose or cellulose derivatives, in at least one solvent selectedfrom the group consisting of tertiary amine oxides, and mixturesthereof, transferring the solution into a coagulation bath by extrudingthe solution through a spinning nozzle by a wet spinning or an air-gapspinning method to form the lignin-containing precursor fibre, whereinthe lignin-containing precursor fibre precipitates when the solution isextruded, stretching the lignin-containing precursor fibre to at least1.1 times its length, at a temperature of at least 60° C. in thecoagulation bath, in air, or in water vapour, and, after stretching,carbonizing the lignin-containing precursor fibre at inert conditionsand at a temperature above approximately 800° C. to form carbon fibers.29. The method of claim 28 further wherein the pH value of thecoagulation bath is between 2 and
 5. 30. The method of claim 28 furthercomprising: subjecting the carbon fibers to a water vapor treatment at atemperature greater than 200° C.
 31. The method of claim 28 furthercomprising: stabilizing the lignin-containing precursor fibre at atemperature between 100 and 600° C. before carbonizing thelignin-containing precursor fibre.